gittensor-impact-card.mjs's two api.gittensor.io/gittensor.io fetches have no request timeout

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Context

scripts/gittensor-impact-card.mjs renders the README "Gittensor impact" SVG card by fetching data from
api.gittensor.io and gittensor.io at build/CI time. Two of its network calls have no timeout:

• fetchJson(url) (lines 50-56) calls fetch(url, { headers: {...} }) with no signal at all — used for
  both https://api.gittensor.io/repos/${encoded}/impact and .../prs (lines 214-216).
• The gt-logo fetch at line 217: fetch("https://gittensor.io/gt-logo.svg").then((r) => r.text()) — also no
  signal.

Every other outbound fetch() call already exercised by this script family sets an explicit timeout via
AbortSignal.timeout(...):

• scripts/smoke-observability-metrics.mjs (lines 51/57/64)
• scripts/smoke-observability-traces.mjs (lines 52/58)
• scripts/check-mcp-release-due.mjs (line 184, GITHUB_REQUEST_TIMEOUT_MS)
• scripts/smoke-production.mjs / scripts/load-test-worker.mjs (both use an AbortController +
  setTimeout)
• src/github/client.ts (GITHUB_FETCH_TIMEOUT_MS), src/github/public.ts
  (GITHUB_PUBLIC_FETCH_TIMEOUT_MS), src/github/migration-tree.ts (GITHUB_FETCH_TIMEOUT_MS)

This is the same "no timeout on an external call, unlike every sibling fetcher" class of bug already fixed
across the repo (#7070 qdrant-vectorize.ts, #7071 fetchRepoFocusManifestFile, #7072 fetchShotContentBlock,
#7014 three release/observability scripts, #7007 the extension's sync fetch, #6988 oauth-device-flow.js) —
scripts/gittensor-impact-card.mjs was missed by that sweep. Without a timeout, a hung api.gittensor.io or
gittensor.io response hangs the README-card regeneration job indefinitely instead of failing fast.

Requirements

• Add an explicit request timeout (AbortSignal.timeout(...)) to every fetch() call in
  scripts/gittensor-impact-card.mjs: the two calls inside fetchJson (both the impact and prs requests
  route through it) and the standalone gt-logo.svg fetch at line 217.
• Follow this repo's existing convention: a single named timeout constant (e.g.
  GITTENSOR_IMPACT_CARD_FETCH_TIMEOUT_MS) reused by all three call sites, matching how
  GITHUB_FETCH_TIMEOUT_MS / GITHUB_PUBLIC_FETCH_TIMEOUT_MS are defined once and reused in
  src/github/client.ts / src/github/public.ts.
• On a timeout/abort, the script must still fail loudly (matching its current main().catch(...) ->
  process.exit(1) behavior) rather than hanging or swallowing the error.
• Do not change the script's non-error-path output shape (the generated SVG) or its CLI usage
  (node scripts/gittensor-impact-card.mjs <owner/repo> <out-file.svg>).

Deliverables

• A shared timeout constant used by fetchJson's fetch call and the gt-logo.svg fetch.
• Both call sites pass signal: AbortSignal.timeout(...) using that constant.
• A regression test (or an addition to any existing test for this script) that stubs a hanging fetch
  and asserts the call aborts within the configured timeout instead of hanging.

Test Coverage Requirements

scripts/** is explicitly excluded from the Codecov ignore: list in codecov.yml (- "scripts/**"), so
codecov/patch does not gate this file — it is not unit-coverable via the Codecov patch gate. Add or
extend a vitest unit test that exercises fetchJson (and/or the module's exported pure helpers, if any are
extracted for testability) with a stubbed/injectable fetch that never resolves, and assert the call rejects
via the configured AbortSignal.timeout rather than hanging the test run. Run locally via
npm run test:coverage per this repo's contributor workflow even though Codecov itself won't gate it.

Expected Outcome

scripts/gittensor-impact-card.mjs can no longer hang indefinitely on a slow/unresponsive
api.gittensor.io or gittensor.io response — every outbound fetch in the script fails fast on a bounded
timeout, consistent with every other external-fetch script in this repo.

Links & Resources

• scripts/gittensor-impact-card.mjs (lines 50-56, 213-218)
• Precedent: src/github/client.ts (GITHUB_FETCH_TIMEOUT_MS), src/github/public.ts
  (GITHUB_PUBLIC_FETCH_TIMEOUT_MS), src/github/migration-tree.ts (GITHUB_FETCH_TIMEOUT_MS)
• Same bug class already fixed elsewhere: fetchShotContentBlock's screenshot fetch has no AbortSignal.timeout, unlike this file's own resolveShotUrl fetch #7070, fetchRepoFocusManifestFile's GitHub raw-content fetch has no AbortSignal.timeout, unlike its review/signals siblings #7071, qdrant-vectorize.ts's 5 Qdrant REST calls have no AbortSignal.timeout, unlike every other self-host external-fetch adapter #7072, 3 unattended release/observability scripts have no fetch timeout, unlike sibling scripts #7014, Extension's syncRankedCandidatesFromMinerUi fetch has no timeout #7007, oauth-device-flow.js's GitHub fetches have no request timeout #6988

[linear-code]

JSO-5009